1. Field of the Invention
This invention relates to artificial seismic sources used in geophysical marine prospecting.
2. Description of the Prior Art
In French Pat. No. 6,926,481 and its additions (Nos. 7,028,731 and 7,715,959), a method and an apparatus was described for producing a shock wave inside a mass of water in view of geophysical studies of the seismic prospecting type. According to this technique, water vapour is produced at a predetermined temperature and pressure, and a certain volume of water vapour is rapidly released at the required depth into the mass of water, which volume of water vapour expands into a single large bubble which then condenses vigorously, thus producing an implosion which generates a high-energy shock wave.
This seismic marine source, which has been used for several years, has considerable advantages: the production of a reproducible of acoustic wave ("signature"), which is advantageous for seismic studies; and absence of pollution. However, it requires vapour which is under a fairly high pressure (usually from 50 to 100 bars); also, the expansion of the bubble is accompanied by an additional acoustic signal which precedes the implosion itself. Although it is known that, by means of complex mathematical processes, it is possible to compensate for the fact that the signature of the seismic source is not a pure peak, the additional acoustic signal which precedes the peak proves to be inconvenient in certain cases.